I think it's a trick question, seeing as he is skating (so friction is negligible) and moving at a constant velocity (no acceleration) he isn't exerting any more force, which seems to work conceptually, but the problem states he is actively moving the poles so he obviously is exerting a force so maybe it is a trick question...

With friction this is a far more complex question than we are given data for. We would need to know not only the coefficient of friction for the skis, but also data on the poles such as the angle at which they push off the ground since this would lighten the force on the skis. Ideally this would be related as a periodic function of time.

Staff: Mentor

With friction this is a far more complex question than we are given data for. We would need to know not only the coefficient of friction for the skis, but also data on the poles such as the angle at which they push off the ground since this would lighten the force on the skis. Ideally this would be related as a periodic function of time.

You are correct that a realistic answer would depend on the how the force of the poles is exerted and would be periodic. But this is meant as a simple problem, so just pretend that the poles only push backwards with no vertical component and that the force is continuously applied. Then the problem is easily solved (albeit naively).